The present invention relates to a method of editing isochronous communication data and an edit controlling device used therefor in a system of a plurality of electronic devices connected by a communication control bus in which isochronous and asynchronous modes of communication can co-exist for data transmission between the electronic devices.
A system has been considered for connecting a plurality of devices via a communication control bus in which isochronous communication and asynchronous communication can be present together, such as a serial bus according to the IEEE-P1394 standard (hereinafter simply referred to as "P1394 serial bus") for communication between the devices. Details of the P1394 serial bus are disclosed in "IEEE P1394 Serial Bus Specification" (published on Oct. 14, 1993).
FIG. 10 shows an example of such a system. The system comprises four digital video cassette recorders (hereinafter referred to as "D-CAM"), an editing machine (hereinafter referred to as edit controller) and a digital television receiver (hereinafter referred to as "D-TV"). The devices are connected to each other by a cable using the P1394 serial bus transmission. Since each of the devices has a function of relaying signals transmitted via the cable of the P1394 serial bus, the communication system is equivalent to a communication system in which each of the devices is connected to a common P1394 serial bus.
Signal transmission in the devices having a common bus is conducted by the time division multiplexing on every predetermined communication cycle as shown in FIG. 11 (for example, every 125 .mu.s). For the bus management of the communication cycle, a device referred to as a cycle master transmits a synchronization packet indicating the starting point of the communication cycle (cycle start packet: hereinafter referred to as the "CSP") to other devices on the bus. The CSP designates the start of data transmission in the communication cycle. The cycle master is automatically determined by a method specified according to the IEEE-P1394 standard.
Transmission of signals during one communication cycle includes two modes: isochronous communication for periodically transmitting, for example, video data or audio data and asynchronous communication for transmitting, for example, a connection control command, not periodically but as necessary. The isochronous communication data is transmitted prior to the asynchronous communication data. Channel identification 1, 2, 3, . . . , N is provided with each of isochronous communication packets to distinguish among a plurality of isochronous communication packets. After completing the transfer of the isochronous communication packets of all channels, a period of time until the next CSP is used for the transmission of an asynchronous communication packet.
FIG. 12 shows a schematic block diagram for each of the devices of FIG. 10. Each device comprises an operation section 1, a display section 2, a microcontroller 3, an isochronous communication data processing block 4 and a communication layer processing block 5. However, the editing machine has no isochronous communication data processing block 4.
The operation section 1 has keys or the like to enable the user to operate the device. The display section 2 displays, for example, the operational state of the device. The microcontroller 3 reads the state of the operation section 1 and prepares various commands for transmitting the desired instructions to other devices. Further, when it receives various types of commands from other devices, the microcontroller 3 controls the isochronous communication data processing block 4 or the communication layer processing block 5 for executing the processing corresponding to the received command. Further, the microcontroller 3 controls the display in the display section 2 in accordance with the operational state of the device.
The isochronous communication data processing block 4 is a recording/regeneration processing section or a tuner section for digital audio/video signals if the device is D-VTR, a monitor section or a tuner section if the device is D-TV, or a recording/regeneration processing section or a camera section for digital audio/video signals if the device is D-CAM.
The communication layer processing block 5 conducts processing operations for converting an isochronous or asynchronous communication packet between the P1394 serial bus format and the format used by the isochronous communication data processing block 4 or the microcontroller 3. The communication layer processing block 5 may also perform arbitration processing for a physical layer and a link layer, such as obtaining or aborting the right to use the P1394 serial bus.
In the communication system of FIG. 10, the editing procedure is conducted, for example, by using D-VCR 1 as a playback machine, and D-VCR 2 as a recording machine via the control of the editing machine. The editing in this case is an assemble mode editing by a so-called 1:1 edit system of dubbing signals regenerated from a video tape (original tape) of a playback machine by superimposing the signals on a portion of an already recorded area on the video tape (master tape) of the recording machine.
In this case, as shown in FIGS. 13C and 13D, the editing machine at first controls the playback machine and the recording machine such that the original tape and master tape are prerolled from their respective regeneration/recording IN points. Then, the editing machine sets the playback machine and the recording machine to the regenerating mode and, subsequently, sets the recording machine to a recording mode simultaneously with the arrival of the IN point. Then, when the required portion is recorded on the master tape, the recording operation is stopped. In this case, external synchronization is applied to the recording machine via a frame sync signal in the regenerated video signals of the playback machine. The operation of the playback machine and the recording machine is controlled such that the instances at which respective tape positions reach the respective IN points coincide with each other.
For conducting such editing with high accuracy, it is necessary for the editing machine to accurately determine tape position information on the playback machine and on the recording machine. It is also necessary for the playback machine and the recording machine to execute an editing control command at the instance designated by the editing machine. Thus, for the editing machine to obtain accurate tape position information on the playback machine and on the recording machine in the system of FIG. 10, it may be necessary to analyze system data added to audio/video data sent by the isochronous communication packet, and to read either an absolute track number (track number appended sequentially from the beginning to the end of the tape to each of the tracks) or a time code. However, for the editing machine to analyze the system data, a hardware equipment is required for separating the system data from the audio/video data and for analyzing the data.
It may also be necessary to request a time code using an inquiry command packet of the asynchronous communication and receive an answer from the corresponding device. However, the time code transmitted by the asynchronous communication packet may sometimes have a delay in relation to the time code in the system data added to the audio/video data transmitted by the isochronous communication packet.
Further, since the command sent from the editing machine to the playback machine and to the recording machine is transmitted by the asynchronous communication packet, there is no time reference for audio/video data. Further, the time at which the editing machine sends a command is different than the time at which the command is actually executed by the playback machine or the recording machine depending on the various conditions such as the type of the command.
Although problems have been described in the case of conducting the editing procedure by the communication system of FIG. 10, similar problems also occur in an editing system in which the editing machine cannot recognize the frame boundary in the video signals in an editing system, for example, as shown in FIG. 14, which comprises a plurality of analog or digital VCRs connected by analog or digital audio/video signal lines and an editing machine, connected to them by control signal lines, for sending and receiving the corresponding command/answer.